Will 14mm into 1/2"-20 UNF 'go' ?

[T i m]

Hi all,

Following the recent thread re 90 deg drills and grinder conversions .. I bought a 13m capacity key'd chuck with 1/2" -20 UNF female thread (with SDS adaptor) from the market today (for +AKM-3) to play with ;-)

Mum and Dad happened in Makro and collected the nutool mains drill and mini grinder combo for +AKM-14.99 (+-Vat) for me (bless) ;-)

So, to make my 90 deg drill I might be able to drill / bore (on the lathe) and tap the chuck out to 14mm then it would screw directly onto the angle driver removing the need for the 'converter' in-between? In this config the 'length' of the whole unit will be about 6" (150mm).

So, from what I can see, the tapping drill for 1/2" UNF is 10.8mm with the outer thread size of about 12.4 mm. I think the tapping drill size for a '14' mm thread is 12mm with a final thread size of about 13.7mm? Assuming I'm right with the numbers do you think I could get away with that?

All the best ..

T i m

[Bob Minchin]

+-ACY-gt+-ADs-Hi all,+-ADw-BR+-AD4- +-ACY-gt+-ADsAPA-BR+-AD4- +-ACY-gt+-ADs-Following the recent thread re 90 deg drills and grinder conversions+-ADw-BR+-AD4- +-ACY-gt+-ADs-.. I bought a 13m capacity key'd chuck with 1/2+-ACY-quot+-ADs- -20 UNF female thread+-ADw-BR+-AD4- +-ACY-gt+-ADs-(with SDS adaptor) from the market today (for +-AKM-3) to play with +-ADs--)+-ADw-BR+-AD4- +-ACY-gt+-ADsAPA-BR+-AD4- +-ACY-gt+-ADs-Mum and Dad happened in Makro and collected the nutool mains drill and+-ADw-BR+-AD4- +-ACY-gt+-ADs-mini grinder combo for +-AKM-14.99 (+--Vat) for me (bless) +-ADs--)+-ADw-BR+-AD4- +-ACY-gt+-ADsAPA-BR+-AD4- +-ACY-gt+-ADs-So, to make my 90 deg drill +-ACY-lt+-ADs-the theory is+-ACY-gt+-ADs- I might be able to drill /+-ADw-BR+-AD4- +-ACY-gt+-ADs-bore (on the lathe) and tap the chuck out to 14mm then it would screw+-ADw-BR+-AD4- +-ACY-gt+-ADs-directly onto the angle driver removing the need for the 'converter'+-ADw-BR+-AD4- +-ACY-gt+-ADs-in-between? In this config the 'length' of the whole unit will be+-ADw-BR+-AD4- +-ACY-gt+-ADs-about 6+-ACY-quot+-ADs- (150mm).+-ADw-BR+-AD4- +-ACY-gt+-ADsAPA-BR+-AD4- +-ACY-gt+-ADs-So, from what I can see, the tapping drill for 1/2+-ACY-quot+-ADs- UNF is 10.8mm with+-ADw-BR+-AD4- +-ACY-gt+-ADs-the outer thread size of about 12.4 mm. I think the tapping drill size+-ADw-BR+-AD4- +-ACY-gt+-ADs-for a '14' mm thread is 12mm with a final thread size of about 13.7mm?+-ADw-BR+-AD4- +-ACY-gt+-ADs-Assuming I'm right with the numbers do you think I could get away with+-ADw-BR+-AD4- +-ACY-gt+-ADs-that?+-ADw-BR+-AD4- +-ACY-gt+-ADsAPA-BR+-AD4- +-ACY-gt+-ADs-All the best ..+-ADw-BR+-AD4- +-ACY-gt+-ADsAPA-BR+-AD4- +-ACY-gt+-ADs-T i m+-ADw-BR+-AD4- +-ACY-gt+-ADs-

Perfectly feasible if done with care Keeping everything concentric will be important. CHuck a piece of scrap 3/4+ACI- or similar steel bar in the three jaw, turn down to 1/2+ACI- and fit the drill chuck onto this and tighten using all three key holes in turn and tighten some more+ACE- yuo do not want this moving later+ACE- Bore out the back of the drill chuck then screw cut most of the material for the 14mm thread. If your lathe is imperial, get the nearest you can with change wheels and gearbox but don't disengage the clasp nuts between passes. Instead stop the motor and wind back by hand/under power otherwise you will not be able to pick up the cut.

Depending on how close you can get to the correct pitch, stop before the whole thread is cut and finish off with a plug tap.

The reason for the screw cutting is simple that there is quite a lot of meat to remove on a 14mm thread and hand tapping a blind hole this size will be quite hard work and risks the work slipping and loss of concentricity.

run out in a drill at angle grinder speeds will be bad news if not downright dangerous.

You might want to find a way of putting a couple of spanner flats on the chuck body (not the tightening ring) so you can get it off the angle grinder as it will tighten in use. Greasing the thread will help too.

Good Luck

Bob

[T i m]

[T] Hi Bob, sorry, I nearly missed your kind reply .. ;-(

[T] Is this to ensure the internal concentricity of the chuck and it's jaws? There is quite a bit of nice parallel steel on the outside nose of the chuck that would give a nice hold?

[T] Ah, the boring bit I can do easily but not sure about the screwcutting. Well, I know what I'm supposed to do just not done it much on this ML10? I have a draw full of gears if that's any help ;-)

If your lathe is imperial,

[T] It is .. I bought it a long time ago ...

get the nearest you can with

[T] Understood

[T] The thread hole is blind so this is a 'tricky' operation isn't it? (made easier by going very slowly ..?)

[T] Ok that's the tricky bit I mentioned ;-) Even running the thread past the last run can be 'akward' can't it?

and finish off with a plug tap.

[T] Ok ..

[T] Indeed. On smaller threads I have put the taper tap in the drill chuck in the unlocked tailstock (so it slides on the bed). I then work the job onto the tap by hand whilst it is supported in the tailstock?

[T] Indeed! I am also going to buy / build a speed controller and will fit an electronic 'stop' to a reasonable working rpm.

[T] Doh!

so you can get it off the angle grinder

[T] Good idea ... I knew I should have bought that milling machine! Mind you, I can probably rig the chuck on the cross-slide and put a mill in the 3 jaw (it dosen't have to be thou perfect for a spanner eh?) If the thread comes out a bit 'loose' I might tighten and epoxy the chuck on (the Grinder cost me +AKM-5 ..) ?

[T] Thanks Bob .. I'll nead it!

All the best ..

T i m

p.s. Am I going to be clear tapping 14mm into a hole threaded 1/2" UNF-20 ( or will I have some of the UNF still showing?)